The district attorney’s office in Orange County, Calif., has nearly quadrupled its DNA database over the past nine months, to about 15,000 individual profiles, and officials say they hope to start using it to identify criminal suspects by early next year.

The agency’s effort to build a database exempt from the rules that govern state and national DNA repositories has made Orange County unique among local governments in California. Much of the rapid growth has come from cases in which prosecutors drop charges against low-level offenders who agree to submit DNA samples.

Critics have questioned whether it’s appropriate to gather DNA from people not convicted of a crime.

About half the samples in the database are from people who have accepted that offer, said Susan Kang Schroeder, a spokeswoman for the district attorney’s office. People charged with nonviolent misdemeanors such as petty theft or trespassing are allowed to donate their DNA and have their cases dropped. In January, the option was extended to those charged with certain personal-use drug possession felonies.

The program has won support from some defense attorneys and others.

“People that are coming into the system for the very first time don’t get a case filed against them,” said Carol Lavacot, a defense attorney based in Irvine, Calif. “It’s a second chance.”

The program doesn’t sit well with others, who express concern over who gets offered the deal, how the data will be managed and what it will be used for.

The district attorney’s database is “highly unusual” because it is not managed by an accredited crime lab, said Beth Greene, president of the American Society of Crime Lab Directors and chief of forensic services at the Florida Department of Law Enforcement’s Pensacola lab.

“This whole concept of voluntary sample building and getting people to plead for less is not the way state databases are run,” she said. “There are no special arrangements made. You get simple samples collected per the law. In our opinion that safeguards the samples in the database.”

Some legal observers question whether people would be targeted on low-level technical crimes in an effort to expand the database.

“That seems backward,” said Jennifer Mnookin, a professor at the University of California, Los Angeles, law school. “I’d like to see what institutional protections they’re putting into place.”

But Barry Fisher, retired crime lab director for the Los Angeles County Sheriff’s Department, said the debate over the use of DNA in courthouse deals is more a public policy issue than a civil liberties one. The Orange County agency makes a compelling argument that it is trying to use the technology to identify those who have not made it into the state or federal databases, he said.

People who accept the deal sign a waiver that explains the rights they are giving up and the fact that their sample will be put in the Orange County district attorney’s DNA database, which is separate from the Department of Justice database.